Under Branding > Display Content, you can set your content to either appear behind or below the navigation. The 'Straight on Top' option will make your navbar transparent so your content fills the entire screen starting at the top of the page.
The 'Straight on Top' option is ideal when you are not using a Cover section but you want your navigation bar to be transparent.
Page content set to appear after navigation:
Page content set to appear straight on top: